The development of thin-film transistors employing an organic semiconductor gradually began to become more active in the latter half of the 1980s, and has in recent years reached the stage where the thin-film transistor characteristics of amorphous silicon can be exceeded for basic performance. Organic materials are easily worked, and because they have a high affinity with the plastic substrates by use of which thin-film FETs are usually formed, the use of an organic material as the active semiconductor layer in a thin-film device is desirable. Examples of the organic semiconductor include the acenes disclosed in Japanese Patent Application Laid-Open No. H05-55568 such as pentacene and tetracene; the low-molecular-weight compounds disclosed in Japanese Patent Application Laid-Open No. H05-190877 such as phthalocyanines including lead phthalocyanine, perylene and tetracarboxylic acid derivatives thereof; and the polymer compounds disclosed in Japanese Patent Application Laid-Open No. H08-264805, such as aromatic oligomers typified by thiophene hexamers referred to as α-thienyl or sexythiophene, as well as polythiophene polythienylenevinylene and poly-p-phenylenevinylene. (Many of these compounds are also disclosed in Advanced Materials, Vol. 2, p. 99-117, 2002.)
Characteristics such as electrical conductivity and semiconductivity, which are required for using these compounds for the active layer to produce a device, largely depend on the crystallinity and orientation of the material, in addition to the purity of the material. Because those compounds having an extended n-conjugated system, for example pentacene, have a high crystallinity and are insoluble in solvents, thin-films thereof have been formed by using a vacuum-deposition process. Although it is known in this case that a high mobility is attained, the handling of such compounds has been difficult because pentacene, for example, will quickly be degraded by oxygen or moisture in the air. On the other hand, applied development of organic semiconductors using a π-conjugated polymer as an organic semiconductor film has been progressing owing to the fact that such compounds have excellent formability, such as being easily formed into a thin-film by a solution-coating process or the like (“Japanese Journal of Applied Physics”, Japan Society of Applied Physics, Vol. 30, p. 596-598, 1991). In the case of π-conjugated polymers, it is known that the state, of structural arrangement of molecular chains have a large influence on the electrical conductive properties. Similarly, it has been reported that the field-effect mobility of π-conjugated polymer field effect transistors largely depends on the state of structural arrangement of molecular chains in semiconductor layers (“Nature”, Nature Publishing Group, Vol. 401, p. 685-687, 1999). However, because the arrangement of molecular chains of π-conjugated polymers are effected in a period from coating of a solution to drying of the solution, there is a possibility that the state of arrangement of molecular chains may vary largely depending on changes in environment or coating methods. There has also been reported an FET using a film prepared by forming a thin film of a soluble precursor of pentacene by coating and transforming the precursor to pentacene by heat-treatment (“Advanced Materials”, WILLEY-VCH Verlag GmbH, Vol. 11, p. 480-483, 1999). In this case, the conversion to pentacene has required a high-temperature treatment, and eliminated components with a large mass have had to be removed under reduced pressure. Further, it has been reported that tetrabenzoporphyrin obtained by heating at 200° C. porphyrin having bulky bicyclo[2.2.2]octadiene skeletons fused is useful as an organic semiconductor (Proceedings of the 81st Annual Spring Meeting of the Chemical Society of Japan, 2002, II, p. 990, 2F9-14; Japanese Patent Application Laid-Open No. 2003-304014; Japanese Patent Application Laid-Open No. 2004-6750). However, in this case, in order to obtain a crystalline film showing stable characteristics, a high calcinating temperature was required.